The present invention relates to an apparatus and method for measuring the forces and distribution of forces on a user""s foot and utilizing this data in combination with other factors to manufacture a custom designed orthotic inlay with an automated fabrication machine.
Footwear has been utilized by mankind for thousands of years for protection from rough terrain, thermal extremes, and other hazards. Although primarily utilitarian in nature, footwear construction and design are often influenced by custom and aesthetics. In recent times, the design of footwear has focused more on achieving maximum comfort in general and specialized construction for athletic uses.
Regardless of the protection and other benefits of footwear, they also are frequently a source of discomfort and, sometimes, trauma. Although footwear manufacturers often attempt to produce comfortable footwear, manufacturing practice and distribution methods effectively limit the range of sizes and shapes available to the purchaser. Women""s high heeled shoes, for example, are frequently uncomfortable and can lead to acquired problems of the foot. Even regular Oxford style footwear with a standard heel and adequate room for the foot is frequently uncomfortable. This is due to the limited size and shape of footwear available for a limitless variety of human foot sizes and shapes. There are frequently size differences between the feet of the same individual and even the same foot between the heel and forefoot. For example, the right foot may require a size 10-medium shoe while the left requires a size nine. Furthermore, the individual""s right heel may be smaller than the predicated standard forefoot to heel width for the size 10-medium shoe. Since footwear is sold in pairs of the same size (length and width), the general rule is to obtain the largest size that will fit both feet and hope for the best. Since neither foot, in the above example, is properly fitted, abnormal loads and movement within the footwear during ambulation can be anticipated.
Another issue not addressed by footwear manufacturers and not readily appreciated by the consumer but which has a direct bearing on comfort is the concept of body weight to foot size ratio. For example, an inlay specification for a person weighing 140 pounds and wearing a size 10 shoe compared to another individual who weighs 200 pounds with the same size footwear is significantly different.
Producing comfortable footwear is made more difficult by the fact that the structure and shape of both the foot and footwear changes during movement which can generate complex plantar pressures. Local areas of high plantar pressure frequently causes pain forcing an individual to adopt unusual ambulation patterns which may, in turn, cause secondary problems in the foot, leg or back. Prolonged areas of high local pressure can result in painful blisters and skin thickening or callus formation. When this is coupled with loss of protective sensation, such as in diabetics, prolonged abnormal pressures can result in ulceration, bone infection and ultimately, amputation. The measurement of the magnitude and distribution of forces present on the plantar surface of the patient""s foot during ambulation is described in detail in the Applicants"" U.S. Pat. Nos. 5,678,448 and 5,323,650, which are incorporated herein in their entirety by reference.
Foot problems increase with age and may include gradual destruction, over time, of the protective fat pads located under the bony heel and under each of the toe bases. This coupled with arthritic changes in the foot results in a less adaptable foot during ambulation subject to increasing discomfort and secondary changes to include limited joint motion and muscle imbalance.
Footwear manufacturers, depending on intended use, vary sole rigidity which tends to disperse high local pressures generated by sharp objects. They generally provide a thin, inadequate, generic pad for the plantar foot for esthetics. From the above discussion, it should be obvious that a specifically designed interface (inlay) between the plantar foot and footwear is needed to match the unique foot to the generic footwear which objectively address the above issues.
Recognizing the need for an interface between the plantar foot and footwear is, of course, not new. In 1865, Everett H. Dunbar designed the leather lift. In 1905, Dr. Royal Whitman developed the first medical inlay referred to as the whittman plate. In 1910, Dr. William Scholl commercialized the first arch support, the Foot Eazer. Custom inlays (orthotics) began to be developed during the 1930""s but it wasn""t until the 1980""s that semi-automated fabrication systems began to appear. These systems generally automate the process of making the positive mold then resort to traditional inlay fabrication techniques.
Current custom inlay design is based on the shape of the bottom of the foot and to a lessor extent, the inside shape of footwear. Traditionally, a cast mold is made by pouring plaster into a foam impression of the planter foot. Various moldable materials are pressure and/or heat fitted to the cast mold. Highly skilled inlay fabricators (podiatrist, orthotist or pedorthist) then fit the molded inlay product to the foot and shoe. Depending on the skill of the fabricator, an inlay can be fitted to achieve a fairly high degree of comfort based on trial and error methods. Unfortunately, these custom inlays or orthotics require 3 to 4 hours of labor over several days and multiple return visits by the wearer to make the necessary adjustments. Custom inlays are, therefore, time intensive to fabricate, expensive and are at best only an educated estimate of the ideal fit. The effects of changes in the foot and footwear shape during ambulation are ignored, as well as the actual forces which are being exerted on the foot.
An automated method as taught by Schartz (U.S. Pat. No. 4,517,696) and Rolloff (U.S. Pat. Nos. 4,876,758 and 5,640,779) uses a device which generates a numeric foot shape description by use of closely spaced pins pushing against the plantar surface of the foot while the individual is standing or seated. The foot being measured rests on a firm flat platform, and the pins are pushed against the foot with varying pressure, distorting the foot in the process. The displacement of each pin is separately expressed as a number. Thus, this group of numbers represents the shape of the foot. This numeric information is then suitably processed and used as input to a numeric controlled machine to produce inlays. This method is flawed in several respects. First, it modifies the actual shape of the foot during measurement. Second, the process only accumulates data on a stationary foot as opposed to measurements on a foot in motion. These methods do not provide true pressure mapping of the plantar foot. The fabrication component of this method uses pre-formed blanks and only mills the top side. The tool path is a first traverse of the perimeter of the milled area with subsequent traverses offset to the center of the work piece. This is a traditional fabrication process used for milling a rigid work piece. However, it is an inferior process for use with soft materials due to problems associated with holding the work piece and debris collection issues. Further, the use of preformed blanks creates an inventory problem because each shoe brand, style, and size is a separate stock item.
Another process requires that an individual take several steps while barefoot on a capacitive matrix force plate, as taught by U.S. Pat. No. 5,088,503 to Serts. A digital pressure map of the plantar foot is developed and augmented by fabricator input. The resultant prescription file is sent by modem to a central facility where a semi-rigid orthotic inlay is manually fabricated. This process has several significant limitations. There is no in-shoe pressure data obtained, the entire ambulation cycle is not studied, the sample size is limited to just a few steps on a force plate and the very process of stepping on a force plate at a specific location affects the measurements and renders them invalid for use in developing an inlay specification.
A non-automated method has further been utilized by inserting a pre-heated (softened) thermoplastic material between the footwear and the user""s plantar foot. When the individual stands, the soft material migrates from any high pressure area to a low pressure area. After cooling, the insert retains the new shape. This inlay functions to hold the plantar foot in a preset neutral position but achieves very little plantar pressure re-distribution. Again, only the non-dynamic stance phase of foot pressure is addressed, i.e. non ambulatory, and represents, at best, a holding form for the foot.
There is thus a significant need for an orthotic inlay which reduces excessive differential plantar pressures, provides a significant reduction in fabrication time, can be designed to match the foot to specific footwear not only while standing but also while engaged in any form of ambulation, and can be produced in a manner to reduce fabrication error and provide a means to objectively document the post-fit plantar pressures. An apparatus and method describing such a system is described hereinbelow.
It is thus one object of the present invention to provide an improved method for creating an orthotic inlay by utilizing force distribution measurements and generating an optimal force distribution profile. These force distribution measurements are obtained during the ambulatory functions of a foot, which is used herein describe the non-static positioning and movement of a foot during walking, running, jumping, etc.
To avoid any misunderstanding, the word xe2x80x9cpressurexe2x80x9d as used herein is pressure in the mechanical sense meaning xe2x80x9cforce per unit areaxe2x80x9d. Generally, the human body only perceives and is affected by pressure differences. An example of a pressure differential is a barefooted person bringing a heel down on a pebble or a hard flat surface. In this event, a substantial portion of the person""s weight will be concentrated at the contact area between the pebble and the foot, and the resultant extreme pressure differential will cause pain and potential trauma. Thus, the shape and mechanical nature of objects forced together determines the pressure distribution between the objects. In the instance of two rigid objects, computation of the pressure is simple because the contact areas are constant. In the instance of two resilient objects, the issue is much more complex due to increased force causing an increase in the contact area. The human foot is a resilient object, and so is most footwear. Yet, the shapes of both when loaded determine the distribution of pressure between the two. If the shape of either is changed, then the pressure distribution changes. Hence, there is a direct, but complex, correlation between loaded shoe and foot shapes and pressure distribution.
The method of the present invention deals directly with the pressure distribution pattern on the plantar surface of the foot during ambulation to generate an inlay shape which redistributes pressures to a more advantageous pattern. The inlay shape is a mathematical function of the measured pressure distribution during ambulation, the desired pressure distribution, and the shape of the footwear.
Generation of a desired pressure distribution pattern is thus a necessary prerequisite to inlay shape generation. Although usually unexpressed, redistribution of pressure is the goal of any inlay fabrication method. With the method of the present invention, development of a desired pressure distribution follows receipt and analysis of all aspects of the measurement data by use of analysis tools which are essential parts of the system. These analysis tools may include, but are not limited to, displays of, a frame by frame view of the direct measurement data, a force versus time plot for each foot fall, a centroid of forces track for each foot fall, and composites, averages, and derivatives of each and all of the above. However, the fundamental element of the method of the present invention is pressure redistribution to reduce peak pressures through modification of the inlay shape, and underlying this is a computer routine to achieve pressure leveling within user-defined areas of the plantar surface of the foot.
Pressure leveling is achieved by increasing the inlay thickness in areas of low measured pressure. Conversely, the inlay is thinner in areas of greater measured pressure. At peak measured pressure areas, the inlay has a minimum thickness. The bottom shape of the inlay must reasonably fit, or match, the footwear. The top shape, or elevation (ST) at any single point is:
ST=SB+Dxe2x88x92Cxc3x97Txe2x80x83xe2x80x831.0
where:
SB is the elevation of the bottom of the inlay
D is the desired pressure
C is the composite pressure pattern
T is the translation factor
Note that elevation is a vertical distance from a datum plane. xe2x80x9cTxe2x80x9d is empirically derived. The above may only be applied to local areas having uniform load bearing capability. Different areas of the foot have different capabilities. For example, the instep cannot tolerate as much pressure as the heel. Consequently, the total plantar surface area of the foot must be subdivided into appropriate local areas and 1.0 above must be applied with different xe2x80x9cTxe2x80x9d factors for each area.
Because the above can change the relative position of the skeletal elements of the foot, an additional elevation factor is necessary.
ST=SB+Dxe2x88x92Cxc3x97T+Pxe2x80x83xe2x80x831.1
where:
P is an added, or subtracted, depth
Note that the xe2x80x9cPxe2x80x9d factor varies between local areas.
The xe2x80x9cPxe2x80x9d factor can serve another important function in defining the shape of the inlay. It is an appropriate variable to accomplish adjustments to the foot""s posture when a review of the measurement data as described above indicates such to be necessary. An example of this is a fallen metatarsal arch. In this instance, a high pressure is seen proximal to the second through fourth metatarsal heads. Without an appropriate xe2x80x9cPxe2x80x9d factor adjustment to this local area, an inappropriate inlay shape could result.
Once the inlay shape is determined, the numeric specification can be used to control automated equipment to fabricate the inlay. The ideal material for inlay fabrication must be resilient to some degree. If the inlay is to be fabricated by machining, it is preferably machined on all sides. Consequently, the present invention includes a means to support all inlay material blank pieces on all six sides and a sequence of milling to assure maximum stability of the work piece, maximize efficiency of debris removal, and achieve adequate precision.
The advantages of the method of the present invention include but are not limited to reduced space requirements for data collection and fabrication, objective measurement capability to minimize guesswork, increased speed of fabrication, and the elimination of most of the hand work mess, and clutter of traditional custom inlay fabrication. Further, manipulation of the inlay shape prior to fabrication, evaluation of shape and data files either locally or at a remote location, the capability to collect data for research purposes, and post-fit pressure analysis is provided. Additionally another significant advantage is that it allows the Fabricator to directly observe, manage, adjust, and work with a desired pressure distribution as a means of creating an inlay shape prior to actual fabrication.
Thus, in one aspect of the present invention, a method for fabricating an orthotic inlay for insertion into footwear is provided, comprising:
obtaining force data which is indicative of the magnitude and distribution of forces present on the plantar surface of a foot during ambulatory functions;
generating optimum orthotic shape inlay data based on said force data; and
fabricating said orthotic inlay using said orthotic inlay shape data.